1. Field of the Invention
The present invention relates to a 4-cycle engine which produces an exhaust having a relatively low amount of hydrocarbons, carbon monoxide, or the like.
2. Description of the Prior Art
One example of a 4-cycle engine in the prior art will be described with reference to FIG. 9 which is a cross-sectional view of a known 4-cycle internal combustion engine.
In this figure, reference numeral 1 designates a cylinder, numeral 2 designates a crankcase, numeral 3 designates a cylinder head, number 4 designates a piston, numeral 5 designates a crankshaft, numeral 6 designates a connecting rod, numeral 33 designates a cam shaft, numeral 37 designates an intake valve (an exhaust valve also has a similar configuration), and numeral 16 designates an ignition plug. Because these members are all principal parts of an internal combustion engine and well known, a further description thereof will be omitted. Reference numeral 40 designates lubricant oil which is reserved within the crankcase 8. Reference numeral 41 designates an oil dipper which is provided at a larger end portion of the connecting rod 6. When the piston 4 is proximate the bottom dead point, the oil dipper 41 contacts the lubricant oil 40. Reference numeral 7 designates a combustion chamber which is provided by a recess in the cylinder head 3 and is bounded by the cylinder 1 and piston 4. Reference numeral 34 designates a tappet, numeral 35 designates a push rod, and numeral 36 designates a rocker arm, which form a well-known valve moving mechanism jointly with the cam shaft 33 for opening and closing the intake valve 37 and an exhaust valve (not shown).
In operation, movement of the piston 4 opens the intake valve 37 via the cam shaft 33, the tappet 34, the push rod 35 and the rocker arm 36 and fresh gas is drawn into the cylinder 1. After the compression, ignition-combustion and expansion strokes have been carried out in a well-known manner, the exhaust valve (not shown) is opened to facilitate the discharge of exhaust, and one period is finished. As a result of vertical movement and rocking motion of the connecting rod 6, the oil dipper 41 splashes the oil 40 into the crankcase 8, and hence portions of the engine in sliding and rotary engagement are lubricated by the splashed oil. In another type of engine, in which an oil dipper is not employed, a lubricant oil pump is provided to circulate the lubricant oil reserved in the crankcase.
However, in the case of the above-described 4-cycle engines in the prior art, the orientation of the engines is limited due to the fact that lubricant oil is to be reserved at the bottom portion of the crankcase. That is, if the engine were to be operated while being tilted extremely, an oil dipper could not reach the lubricant oil, and hence there could be no distribution of lubricant oil. On the contrary, if the oil surface is too high relative to the oil dipper, a large amount of lubricant oil will be consumed due to excessive splashing. Accordingly, a 4-cycle engine cannot be used in a hand-held machine such as a hedge cutter, a chain saw or the like. The engines used for these applications are strictly 2-cycle engines. However, in view of thermal efficiency and exhaust gas, 2-cycle engines have many shortcomings. For instance, the amount of hydrocarbons in the exhaust of a 2-cycle engine is more than 10 times that of a 4-cycle engine.